1. Field of the Invention
The present invention relates to the photoelectron integration technical field, and more particularly, it relates to a sensing (measurement) chip for a refractive index of a long-range surface plasmon polariton applied in the region of photon integration, a sensor and the like.
2. Description of the Background Art
A surface plasmon polariton ((SPP), FIG. 1) is an electromagnetic field transmitted along the interface between a metal and a dielectric, and the amplitude thereof is exponentially attenuated in the dielectric in response to the distance from the interface. The SPP is a kind of surface wave whose electromagnetic field energy is concentrated in the vicinity of the interface between the metal and the dielectric, and hence the electromagnetic field on the metal surface is strong and extremely sensitive to the mode of the surface, particularly a change in the refractive index. Thus, the SPP is widely applied as a biochemical sensor.
As shown in FIG. 1, a conventional biochemical sensor of a surface plasmon polariton applies light 3 to a metal surface 1 easily forming surface plasma and changes the angle of incident light 3, so that the surface plasma is excited only by incident light of a certain specific angle 5. In this case, the power of reflected light 4 abruptly decreases. This specific angle is extremely sensitive to refraction of a substance 2 on a cross boundary of the metal surface, and the refractive index of substance 2 on the cross boundary of the metal surface can be measured by measuring angle 5 of the incident light when the power of the reflected light decreases. This conventional measuring method requires separate components such as a prism and a turntable, and is hence hard to adjust due to a large size. Further, the method is inferior in stability, and at a high cost. Therefore, universalization and application thereof are extremely limited.
When a metal portion is a thin film, two sets of surface plasmon polaritons are formed on an upper surface 101 and a lower surface 102 of the thin film, as shown in FIG. 2. When the thickness of the metal thin film decreases up to a constant degree, the two sets of surface plasmon polaritons are coupled with each other. The electric field distribution of such a coupled wave is mostly concentrated in an upper dielectric 2 and a lower dielectric 6 other than the metal and the coupled wave can be transmitted on the metal surface in a long-range manner with small transmission loss, and hence the same is referred to as long-range surface plasmon polariton (LR-SP). Such a long-range surface plasmon polariton is extremely sensitive to the difference between the refractive indices of upper dielectric 2 and lower dielectric 6 of the metal thin film, and the refractive index can be highly precisely measured when measuring loss of the long-range surface plasmon polariton or (and) a light spot size. However, although this method is highly precise, the measurement range is small, and the structure thereof is not suitable to sealing and practical use, but exerts disadvantageous influence on universalization and application.
As shown in FIG. 3, a chip measurement range can be adjusted by rendering a metal strip-like, adding a buffer layer 3 onto the metal while adding a reference arm 12 and another reference arm 13 to both sides of a measurement-waiting metal 11 and adjusting the thickness of the buffer layer, the chip can be sealed by conforming the same to the reference arms, and the strip-like metal is more suitable to direct excitation of an optical fiber. Transmission loss of such a long-range surface plasmon polariton is extremely sensitive to the difference between the refractive indices of an upper dielectric 7 and a lower dielectric 4 of the strip-like metal. Buffer layer 3 has a refractive indeed substantially identical to that of lower dielectric 4. Transmission loss caused by the difference between the refractive indices of lower dielectric 4 and a sample liquid can be reduced by comprising buffer layer 3. Therefore, an apparatus can sense an antigen-antibody reaction, SNPs, a gene-protein interaction, a cell/protein function, as well as a bio material and a biological reaction such as an associative function in high detection sensitivity. In addition, the buffer layer/metal structure is a structure effective for protecting the metal against damage from the liquid. Therefore, the apparatus can be used in a severer situation. In addition, this structure is suitable in relation to molecular modification. The buffer layer is so introduced that the measurement range and precision can be adjusted, and the refractive index of the liquid or an antigen-antibody reaction of an organism can be measured with high precision in a wide-ranging manner.